Method for removing impurity boron through synergistic reinforcement of biomass and additive for industrial silicon

Abstract

The invention relates to a method for removing impurity boron through synergistic reinforcement of biomass for industrial silicon and an additive, and belongs to the technical field of efficient and clean utilization of resources. The method comprises the following steps: crushing and grinding industrial silicon to obtain powder; and drying the biomass, and grinding to obtain powder. The method comprises the following steps: mixing industrial silicon powder and biomass powder, carrying out preliminary roasting to obtain a mixture A, naturally cooling to room temperature, adding alkali carbonate or hydroxide, uniformly mixing, putting into a high-purity graphite crucible, heating to 1350-2200 DEG C in an inert gas atmosphere, carrying out heat preservation for 0.5-4 hours, naturally cooling to room temperature after heat preservation is finished, and removing surface slag to obtain refined silicon. The removal rate of boron impurities in industrial silicon can reach 87-96%, the impurity removal method which is efficient, low in cost and easy to operate is provided, biomass such as waste coffee shells is used for impurity removal, waste recycling is achieved, and efficient and clean production is achieved.

Description

Technical Field

[0001] The invention relates to a method for removing impurity boron in a coordinated manner using biomass for industrial silicon and an additive, and belongs to the technical field of efficient and clean utilization of resources. Background Art

[0002] Compared with traditional fossil energy, solar energy has obvious advantages. Solar energy is a renewable resource with a wide and long irradiation area, safe and reliable, no noise, no pollution, and absolutely environmentally friendly. American scientists Chabin and Pirson first made practical monocrystalline silicon solar cells at Bell Laboratories in the United States, giving birth to photovoltaic power generation technology that converts sunlight energy into electrical energy. The photovoltaic industry is mainly based on silicon materials. Most photovoltaic modules are made of silicon materials, and the raw material of solar cells is polycrystalline silicon. Industrial silicon is a front-end product and a raw material for high-quality industrial silicon. It is the main raw material for solar cells and is very important. And in the development history of industrial silicon, it is very important in our lives. Whether in the information industry or in new energy products, industrial silicon occupies an important position.

[0003] Boron is one of the most difficult non-metallic impurities to remove in metallurgical-grade silicon and has the greatest impact on battery performance. Since boron is a typical shallow-level acceptor impurity, a small amount of impurity boron in silicon will form BO and Fe-B complex defects with interstitial oxygen and metal impurities. The existence of these defects will reduce the battery life and affect the photoelectric conversion efficiency of the battery. If the boron content in silicon crystals is too high, the Auger recombination rate of silicon materials will increase, and the diffusion length and diffusion rate of minority carriers in silicon will be significantly reduced, which will eventually lead to a decrease in the conversion efficiency of silicon cells. Therefore, in the process of preparing solar-grade silicon by metallurgical methods, the boron content in silicon materials should be reduced as much as possible. Generally speaking, the impurity boron content in the silicon material of polycrystalline silicon solar cells is required to be less than 0.3ppmw.

[0004] Patent 2005800064695 discloses a method for removing boron from silicon, which uses a slag adsorption method and utilizes multiple slag making processes and a large amount of alkali metal carbonate (almost in a 1:1 mass ratio with the raw silicon) to obtain polycrystalline silicon with a boron content of less than 0.3 ppmw. Summary of the invention

[0005] The present invention proposes the present invention for the prior art that there is no relevant record of using a small amount of potassium carbonate and biomass to efficiently remove boron from silicon. Due to the similar physical properties, it is difficult to effectively remove boron impurities in silicon. The present invention uses industrial silicon powder as a raw material, and preliminarily roasts it by mixing it with biomass (coffee shells, tobacco straws, cotton straws, peanut shells, rice straws, wheat straws, corn straws, soybean straws, rice husks), and then crushes the roasted product and grinds and mixes it with additives (potassium carbonate, sodium carbonate, sodium hydroxide, potassium hydroxide), and then performs oxygen-free smelting to efficiently remove boron. The present invention has low cost, small slag making amount, low energy consumption, and realizes efficient utilization of resources.

[0006] The present invention provides a method for removing the impurity boron by synergistically strengthening the biomass and additives for industrial silicon, comprising the following steps:

[0007] (1) crushing and grinding the boron-containing industrial silicon to obtain industrial silicon powder;

[0008] (2) drying and crushing the selected biomass to obtain biomass powder;

[0009] (3) 1-5 wt.% of the mass of industrial silicon powder is added with biomass powder, the added industrial silicon powder and biomass powder are evenly mixed, the temperature is raised to 600-900° C., and roasted for 60-120 min in an oxygen-containing atmosphere to obtain a mixture A;

[0010] (4) Mixing the mixture A and M in step (3) uniformly to obtain a mixture B, heating the mixture B to 1350-2200° C. in an inert atmosphere or a protective atmosphere, keeping the temperature for 0.5-4 hours, and cooling naturally after the end of the temperature keeping; obtaining refined silicon; wherein M is an alkali metal carbonate and / or hydroxide; and the amount of M is 1-10 wt.% of the mass of the mixture A.

[0011] In practical application, after the mixture B in step (4) is cooled to room temperature, the trace slag on the surface of the sample is removed to obtain refined silicon. The residual content of impurity boron in the refined silicon is tested by inductively coupled plasma mass spectrometry.

[0012] In the method for removing the impurity boron by synergistically strengthening the removal of the boron impurity by biomass and additives for industrial silicon of the present invention, the purity of the boron-containing industrial silicon in step (1) is 98.7-99.9%, and the boron content in the boron-containing industrial silicon is greater than 1 ppmw. The present invention can process the boron-containing industrial silicon with a low boron content; and has high efficiency, high boron removal rate, and low reagent dosage. Of course, the processing of the boron-containing industrial silicon with a boron content of more than 80 ppmw is more efficient and has better effect.

[0013] The present invention provides a method for synergistically enhancing the removal of impurity boron by biomass and additives for industrial silicon, wherein the biomass in step (2) is selected from at least one of coffee husks, tobacco straws, cotton straws, peanut shells, rice straws, wheat straws, corn straws, soybean straws, and rice husks. More preferably, it is at least one of coffee husks, cotton straws, peanut shells, rice straws, wheat straws, corn straws, soybean straws, and rice husks, and more preferably, it is at least one of coffee husks, peanut shells, wheat straws, and corn straws. This is also the first discovery and application of the present invention.

[0014] The present invention provides a method for removing impurity boron by synergistically strengthening biomass and additives for industrial silicon. In step (1), the particle size of the obtained industrial silicon powder is

[0015] Preferably, in the method for removing the impurity boron by synergistically strengthening the biomass and additives for industrial silicon of the present invention, in step (3), 2 to 5 wt.% of the mass of industrial silicon powder is prepared; the biomass powder is prepared and mixed evenly. Here, 2 to 5 wt.% of the mass of industrial silicon powder is prepared, and the biomass powder is prepared and mixed evenly; including 2 to 2.5 wt.%, 3 to 3.5%, 2.5 to 3%, 3.5 to 4%, 4% 4.5%, 4.5 to 5%, etc., and the biomass powder is prepared and mixed evenly.

[0016] The present invention provides a method for removing the impurity boron by synergistically strengthening the removal of biomass and additives for industrial silicon. In step (4), the alkali metal carbonate is potassium carbonate and / or sodium carbonate.

[0017] The present invention provides a method for removing impurity boron by synergistically strengthening biomass and additives for industrial silicon, wherein in step (4), the alkali metal hydroxide is sodium hydroxide and / or potassium hydroxide. When applied in industry, M is preferably an alkali metal carbonate.

[0018] Preferably, in the method for synergistically enhancing the removal of impurity boron by biomass and additives for industrial silicon of the present invention, in step (4), the amount of M added is 2 to 10 wt.% of the mass of the mixture A, and more preferably 7 to 10 wt.%.

[0019] The present invention provides a method for removing impurity boron from biomass and additives for industrial silicon, wherein the oxygen-containing condition in step (3) is an air atmosphere; and in step (4), the inert gas is argon. The inert atmosphere in step (4) is an argon atmosphere.

[0020] In the refined silicon obtained in step (4), the remaining content of impurity boron / the content in the boron-containing industrial silicon = 0.03 to 0.06.

[0021] The beneficial effects of the present invention are:

[0022] The present invention attempts for the first time to evenly mix industrial silicon powder with an appropriate amount of biomass powder, then heat it to 600-900°C, roast it in an oxygen-containing atmosphere (preferably an air atmosphere) for 60-120 minutes to obtain a mixture A, and then evenly mix the mixture A with an appropriate amount of M to obtain a mixture B, and heat the mixture B to 1350-2200°C in an inert atmosphere or a protective atmosphere, keep it warm for 0.5-4 hours, and cool it down naturally after the insulation ends; to obtain refined silicon; the M is an alkali metal carbonate and / or hydroxide. The present invention does not need to introduce an additional slag-making agent (such as a large amount of silicon dioxide) for slag making, has a significant B removal effect, a simple operating process, low equipment requirements, low cost, low energy consumption, low pollution, and is environmentally friendly. In addition, the present invention has obvious advantages in treating boron-containing industrial silicon with a boron content of more than 80ppmw. Whether it is the processing speed or the boron removal rate of one-time processing, the present invention is far superior to the prior art, and the slag production of the present invention is extremely low. DETAILED DESCRIPTION

[0023] The present invention is further described in detail below in conjunction with specific implementation modes, but the protection scope of the present invention is not limited to the described contents.

[0024] Embodiment 1:

[0025] A method for removing impurity boron by synergistically strengthening biomass and additives for industrial silicon, the specific steps are as follows:

[0026] (1) crushing and grinding 10 g of block industrial silicon with a boron content of 100.46 ppmw and a purity of 99.9% to obtain industrial silicon powder (particle size distribution of 75-150 μm);

[0027] (2) processing the tobacco straw to remove unprocessed tobacco leaves, and then drying and crushing the tobacco straw to obtain tobacco straw powder;

[0028] (3) taking 0.1 g of tobacco straw powder and the industrial silicon powder in step (1), mixing them evenly and loading them into a corundum crucible, placing them in a muffle furnace, heating them to 600° C. at a heating rate of 10° C. / min, and calcining them in air for 90 min to obtain a mixture A;

[0029] (4) Grinding and mixing the mixture A in step (3) and 1 wt.% potassium carbonate in an agate mortar, placing the mixture in a high-purity graphite crucible to obtain a mixture B, placing the mixture B in a muffle furnace, and uniformly heating the mixture to 1500° C. at a rate of 10° C. / min under an argon atmosphere, keeping the temperature for 4 h, and then cooling the mixture naturally after the end of the heat preservation;

[0030] (5) After the mixture B in step (4) is cooled to room temperature, the crucible is broken to remove the slag on the surface of the sample to obtain refined silicon, and the residual content of impurity boron in the refined silicon is tested using an inductively coupled plasma mass spectrometer.

[0031] The content of industrial silicon boron after purification in this embodiment is 11.14 ppmw, and the removal rate is 88.91%.

[0032] Example 1-1

[0033] Other conditions were the same as those in Example 1, except that an equal mass of coffee husk powder was used to replace tobacco straw powder; the content of industrial silicon boron after purification was 7.73 ppmw, and the removal rate was 92.31%.

[0034] Example 1-2

[0035] Other conditions were the same as those in Example 1, except that: the tobacco straw powder was replaced by rice husk powder of equal mass; the content of industrial silicon boron after purification was 15.6 ppmw, and the removal rate was 84.47%.

[0036] Examples 1-3

[0037] The other conditions were the same as those in Example 1, except that: the tobacco straw powder was replaced with an equal mass of cotton straw powder;

[0038] The content of industrial silicon boron after purification is 12.66ppmw, and the removal rate is 87.40%.

[0039] Examples 1-4

[0040] Other conditions were the same as those in Example 1, except that an equal mass of peanut shell powder was used to replace tobacco straw powder; the content of industrial silicon boron after purification was 7.9 ppmw, and the removal rate was 92.14%.

[0041] Examples 1-5

[0042] The other conditions were the same as those in Example 1, except that: the tobacco straw powder was replaced by rice straw powder of equal mass;

[0043] The content of industrial silicon boron after purification is 15.3ppmw, and the removal rate is 84.77%.

[0044] Examples 1-6

[0045] The other conditions were the same as those in Example 1, except that: the tobacco straw powder was replaced with wheat straw powder of equal mass;

[0046] The content of industrial silicon boron after purification is 8.21ppmw, and the removal rate is 91.83%.

[0047] Examples 1-7

[0048] Other conditions were the same as those in Example 1, except that: an equal mass of corn stalk powder was used to replace tobacco stalk powder;

[0049] The content of industrial silicon boron after purification is 8.9ppmw, and the removal rate is 91.14%.

[0050] Examples 1-8

[0051] The other conditions were the same as those in Example 1, except that: the tobacco straw powder was replaced with an equal mass of soybean straw powder;

[0052] The content of industrial silicon boron after purification is 11.72ppmw, and the removal rate is 88.33%.

[0053] Embodiment 2:

[0054] A method for removing impurity boron by synergistically strengthening biomass and additives for industrial silicon, the specific steps are as follows:

[0055] (1) crushing and grinding 10 g of block industrial silicon with a boron content of 86.4 ppmw and a purity of 99.9% to obtain industrial silicon powder (particle size distribution of 75-150 μm);

[0056] (2) drying and crushing the coffee husks to obtain coffee husk powder;

[0057] (3) taking 0.2 g of coffee shell powder and mixing it with the industrial silicon powder in step (1) evenly, loading it into a corundum crucible, placing it in a muffle furnace, heating it to 700° C. at a heating rate of 10° C. / min, and roasting it in air for 70 min to obtain a mixture A;

[0058] (4) Grinding and mixing the mixture A in step (3) and 2 wt.% potassium carbonate in an agate mortar, placing the mixture in a high-purity graphite crucible to obtain a mixture B, placing the mixture B in a muffle furnace, and uniformly heating the mixture to 1550° C. at a rate of 10° C. / min under an argon atmosphere, keeping the temperature for 3.5 h, and then cooling the mixture naturally after the end of the insulation;

[0059] (5) After the mixture B in step (4) is cooled to room temperature, the crucible is broken to remove the slag on the surface of the sample to obtain refined silicon, and the residual content of impurity boron in the refined silicon is tested using an inductively coupled plasma mass spectrometer.

[0060] The content of industrial silicon boron after purification in this embodiment is 5.13 ppmw, and the removal rate is 94.06%.

[0061] Example 3

[0062] A method for removing impurity boron by synergistically strengthening biomass and additives for industrial silicon, the specific steps are as follows:

[0063] (1) crushing and grinding 10 g of block industrial silicon with a boron content of 100.46 ppmw and a purity of 98.7% to obtain industrial silicon powder (particle size distribution of 75-150 μm);

[0064] (2) drying and crushing the rice husk to obtain rice husk powder;

[0065] (3) taking 0.3 g of rice husk powder and mixing it evenly with the industrial silicon powder in step (1), loading it into a corundum crucible, placing it in a muffle furnace, heating it to 800° C. at a heating rate of 10° C. / min, and calcining it in air for 80 min to obtain a mixture A;

[0066] (4) Grinding and mixing the mixture A in step (3) and 3 wt.% sodium carbonate in an agate mortar, placing the mixture in a high-purity graphite crucible to obtain a mixture B, placing the mixture B in a muffle furnace, and uniformly heating it to 1550° C. at a rate of 10° C. / min under an argon atmosphere, keeping the temperature for 3 h, and then cooling it naturally after the end of the insulation;

[0067] (5) After the mixture B in step (4) is cooled to room temperature, the crucible is broken to remove the slag on the surface of the sample to obtain refined silicon, and the residual content of impurity boron in the refined silicon is tested using an inductively coupled plasma mass spectrometer.

[0068] The content of industrial silicon boron after purification in this embodiment is 5.6 ppmw, and the removal rate is 94.43%.

[0069] Example 4

[0070] A method for removing impurity boron by synergistically strengthening biomass and additives for industrial silicon, the specific steps are as follows:

[0071] (1) crushing and grinding 10 g of block industrial silicon with a boron content of 95.7 ppmw and a purity of 98.7% to obtain industrial silicon powder (particle size distribution of 75-150 μm);

[0072] (2) drying and crushing the cotton stalks to obtain cotton stalk powder;

[0073] (3) taking 0.4 g of cotton straw powder and the industrial silicon powder in step (1), mixing them evenly and loading them into a corundum crucible, placing them in a muffle furnace, heating them to 900° C. at a heating rate of 10° C. / min, and calcining them in air for 90 min to obtain a mixture A;

[0074] (4) Grinding and mixing the mixture A in step (3) and 4 wt.% sodium hydroxide in an agate mortar, placing the mixture in a high-purity graphite crucible to obtain a mixture B, placing the mixture B in a muffle furnace, and uniformly heating it to 1600° C. at 10° C. / min under an argon atmosphere, keeping the temperature for 2 h, and then cooling it naturally after the end of the insulation;

[0075] (5) After the mixture B in step (4) is cooled to room temperature, the crucible is broken to remove the slag on the surface of the sample to obtain refined silicon, and the residual content of impurity boron in the refined silicon is tested using an inductively coupled plasma mass spectrometer.

[0076] The content of industrial silicon boron after purification in this embodiment is 8.66 ppmw, and the removal rate is 90.95%.

[0077] Example 5

[0078] A method for removing impurity boron by synergistically strengthening biomass and additives for industrial silicon, the specific steps are as follows:

[0079] (1) crushing and grinding 10 g of block industrial silicon with a boron content of 99 ppmw and a purity of 99.9% to obtain industrial silicon powder (particle size distribution of 75-150 μm);

[0080] (2) drying and crushing the soybean straw to obtain soybean straw powder;

[0081] (3) taking 0.5 g of soybean straw powder and the industrial silicon powder in step (1), mixing them evenly and loading them into a corundum crucible, placing them in a muffle furnace, heating them to 900° C. at a heating rate of 10° C. / min, and calcining them in air for 90 min to obtain a mixture A;

[0082] (4) Grinding and mixing the mixture A in step (3) and 5 wt.% sodium hydroxide in an agate mortar, placing the mixture in a high-purity graphite crucible to obtain a mixture B, placing the mixture B in a muffle furnace, and uniformly heating the mixture to 1700° C. at a rate of 10° C. / min under an argon atmosphere, keeping the temperature for 2.5 h, and then cooling the mixture naturally after the end of the heat preservation;

[0083] (5) After the mixture B in step (4) is cooled to room temperature, the crucible is broken to remove the slag on the surface of the sample to obtain refined silicon, and the residual content of impurity boron in the refined silicon is tested using an inductively coupled plasma mass spectrometer.

[0084] The content of industrial silicon boron after purification in this embodiment is 5.36 ppmw, and the removal rate is 94.59%.

[0085] Example 6

[0086] A method for removing impurity boron by synergistically strengthening biomass and additives for industrial silicon, the specific steps are as follows:

[0087] (1) crushing and grinding 10 g of block industrial silicon with a boron content of 100.46 ppmw and a purity of 98.7% to obtain industrial silicon powder (particle size distribution of 75-150 μm);

[0088] (2) drying and crushing the corn stalks to obtain corn stalk powder;

[0089] (3) taking 0.5 g corn stalk powder and mixing it with the industrial silicon powder in step (1), the mixture was uniformly loaded into a corundum crucible, placed in a muffle furnace, heated to 700° C. at a heating rate of 10° C. / min, and calcined in air for 90 min to obtain a mixture A;

[0090] (4) Grinding and mixing the mixture A in step (3) and 5 wt.% potassium hydroxide in an agate mortar, placing the mixture in a high-purity graphite crucible to obtain a mixture B, placing the mixture B in a muffle furnace, and uniformly heating it to 1800° C. at a rate of 10° C. / min under an argon atmosphere, keeping the temperature for 1.5 h, and then cooling it naturally after the end of the insulation;

[0091] (5) After the mixture B in step (4) is cooled to room temperature, the crucible is broken to remove the slag on the surface of the sample to obtain refined silicon, and the residual content of impurity boron in the refined silicon is tested using an inductively coupled plasma mass spectrometer.

[0092] The content of industrial silicon boron after purification in this embodiment is 12.2 ppmw, and the removal rate is 87.86%.

[0093] Example 7

[0094] A method for removing impurity boron by synergistically strengthening biomass and additives for industrial silicon, the specific steps are as follows:

[0095] (1) crushing and grinding 10 g of block industrial silicon with a boron content of 95.5 ppmw and a purity of 99.9% to obtain industrial silicon powder (particle size distribution of 75-150 μm);

[0096] (2) drying and crushing the peanut shells to obtain peanut shell powder;

[0097] (3) taking 0.3 g of peanut shell powder and mixing it evenly with the industrial silicon powder in step (1), loading it into a corundum crucible, placing it in a muffle furnace, heating it to 600° C. at a heating rate of 10° C. / min, and roasting it in air for 90 min to obtain a mixture A;

[0098] (4) Grinding and mixing the mixture A in step (3) and 8 wt.% sodium carbonate in an agate mortar, placing the mixture in a high-purity graphite crucible to obtain a mixture B, placing the mixture B in a muffle furnace, and uniformly heating it to 1900° C. at a rate of 10° C. / min under an argon atmosphere, keeping the temperature for 1 h, and then cooling it naturally after the end of the heat preservation;

[0099] (5) After the mixture B in step (4) is cooled to room temperature, the crucible is broken to remove the slag on the surface of the sample to obtain refined silicon, and the residual content of impurity boron in the refined silicon is tested using an inductively coupled plasma mass spectrometer.

[0100] The content of industrial silicon boron after purification in this embodiment is 3.5 ppmw, and the removal rate is 96.34%.

[0101] Comparative Example 1:

[0102] A method for removing impurity boron by synergistically strengthening biomass and additives for industrial silicon, the specific steps are as follows:

[0103] (1) crushing and grinding 10 g of block industrial silicon with a boron content of 100.46 ppmw and a purity of 99.9% to obtain industrial silicon powder;

[0104] (2) treating the tobacco straw to remove the untreated tobacco leaves, drying and crushing the tobacco straw to obtain tobacco straw powder, placing the tobacco straw powder in a corundum crucible, placing the crucible in a muffle furnace, heating the crucible to 600° C. at a heating rate of 10° C. / min, and calcining the crucible in air for 90 minutes to obtain ash;

[0105] (3) Grinding and mixing 0.1 g of tobacco straw ash and the industrial silicon powder in step (1) in an agate mortar, placing the mixture in a high-purity graphite crucible to obtain a mixture, placing the mixture in a muffle furnace, and uniformly heating the mixture at 10° C. / min to 1500° C. in an argon atmosphere, keeping the temperature for 4 h, and cooling the mixture naturally after the end of the heat preservation;

[0106] (4) After the temperature of the mixture in step (3) is cooled to room temperature, the crucible is broken to remove the slag on the surface of the sample to obtain refined silicon, and the residual content of impurity boron in the refined silicon is tested using an inductively coupled plasma mass spectrometer.

[0107] The content of industrial silicon boron after purification in this embodiment is 28.78 ppmw, and the removal rate is 71.35%.

[0108] Comparative Example 2:

[0109] A method for removing impurity boron by synergistically strengthening biomass and additives for industrial silicon, the specific steps are as follows:

[0110] (1) crushing and grinding 10 g of block industrial silicon with a boron content of 86.4 ppmw and a purity of 99.9% to obtain industrial silicon powder;

[0111] (2) grinding and mixing the industrial silicon powder and 3 wt.% sodium carbonate in step (1) in an agate mortar, placing the mixture in a high-purity graphite crucible to obtain a mixture A, placing the mixture A in a muffle furnace, and uniformly heating the mixture to 1550° C. at a rate of 10° C. / min under an argon atmosphere, keeping the temperature for 2 h, and then cooling the mixture naturally after the end of the heat preservation;

[0112] (3) After the mixture A in step (2) is cooled to room temperature, the crucible is broken to remove the slag on the surface of the sample to obtain refined silicon, and the residual content of impurity boron in the refined silicon is tested by inductively coupled plasma mass spectrometry.

[0113] The content of industrial silicon boron after purification in this embodiment is 40.19 ppmw, and the removal rate is 53.48%.

[0114] Comparative Example 3

[0115] Other conditions are the same as those in Example 1, except that:

[0116] (2) treating the tobacco straw to remove the untreated tobacco leaves, and then drying and crushing the tobacco straw to obtain tobacco straw powder; placing the tobacco straw powder in a corundum crucible, placing the crucible in a muffle furnace, heating the crucible to 900° C. at a heating rate of 10° C. / min, and calcining the crucible in air for 90 minutes to obtain ash;

[0117] (3) grinding and mixing the industrial silicon powder in step (1) and 1 wt.% of tobacco straw ash in step (2) with 1 wt.% of potassium carbonate in an agate mortar, placing the mixture in a high-purity graphite crucible to obtain a mixture A, placing the mixture A in a muffle furnace, and uniformly heating the mixture to 1500° C. at a rate of 10° C. / min under an argon atmosphere, keeping the temperature for 4 h, and then cooling the mixture naturally after the end of the heat preservation;

[0118] After the mixture A in step (3) is cooled to room temperature, the crucible is broken to remove the slag on the surface of the sample to obtain refined silicon, and the residual content of impurity boron in the refined silicon is tested using an inductively coupled plasma mass spectrometer.

[0119] In this comparative example, the content of industrial silicon boron after purification was 23.64 ppmw, and the removal rate was 76.47%.

[0120] The specific embodiments of the present invention are described in detail above, but the present invention is not limited to the above embodiments. Various changes can be made within the knowledge scope of ordinary technicians in this field without departing from the purpose of the present invention.

Claims

1. A method for removing impurity boron by synergistically strengthening biomass and additives for industrial silicon, characterized in that: The specific steps are as follows: (1) crushing and grinding the boron-containing industrial silicon to obtain industrial silicon powder; (2) drying and crushing the selected biomass to obtain biomass powder; (3) 1-5 wt.% of the mass of industrial silicon powder is added with biomass powder, the added industrial silicon powder and biomass powder are evenly mixed, the temperature is raised to 600-900° C., and roasted for 60-120 min in an oxygen-containing atmosphere to obtain a mixture A; (4) Mixing the mixture A and M in step (3) uniformly to obtain a mixture B, heating the mixture B to 1350-2200° C. in an inert atmosphere or a protective atmosphere, keeping the temperature for 0.5-4 hours, and cooling the mixture after the temperature is maintained to obtain refined silicon; wherein M is an alkali metal carbonate and / or hydroxide; and the amount of M is 1-10 wt.% of the mass of the mixture A.

2. The method for removing impurity boron by synergistically strengthening the removal of biomass and additives for industrial silicon according to claim 1, characterized in that: The purity of the boron-containing industrial silicon in step (1) is 98.7-99.9%, and the boron content in the boron-containing industrial silicon is greater than 1 ppmw.

3. The method for removing impurity boron by synergistically strengthening the removal of boron impurities by using biomass and additives for industrial silicon according to claim 1, characterized in that: In step (2), the biomass is selected from at least one of coffee husks, tobacco straws, cotton straws, peanut shells, rice straws, wheat straws, corn straws, soybean straws and rice husks.

4. The method for removing impurity boron by synergistically strengthening the removal of biomass and additives for industrial silicon according to claim 1, characterized in that: In step (3), 2 to 5 wt.% of the mass of industrial silicon powder is added; and biomass powder is added and mixed evenly.

5. The method for removing impurity boron by synergistically strengthening the removal of boron by biomass and additives for industrial silicon according to claim 1, characterized in that: In step (4), the alkali metal carbonate is potassium carbonate or sodium carbonate.

6. The method for removing impurity boron by synergistically strengthening the removal of biomass and additives for industrial silicon according to claim 1, characterized in that: In step (4), the alkali metal hydroxide is sodium hydroxide or potassium hydroxide.

7. The method for removing impurity boron by synergistically strengthening the removal of biomass and additives for industrial silicon according to claim 1, characterized in that: In the step (4), the grinding and mixing ratio of the mixture A and the alkali metal carbonate or hydroxide is 2 to 10 wt.%, preferably 7 to 10 wt.%.

8. The method for removing impurity boron by synergistically strengthening the removal of biomass and additives for industrial silicon according to claim 1, characterized in that: The oxygen-containing condition in step (3) is an air atmosphere; the inert atmosphere in step (4) is an argon atmosphere.

9. The method for removing impurity boron by synergistically strengthening the removal of biomass and additives for industrial silicon according to claim 1, characterized in that: In the refined silicon obtained in step (4), the remaining content of impurity boron / the content in the boron-containing industrial silicon = 0.03 to 0.06.